netdev - Re: [PATCH] net: allow netdev_wait

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Date:	Wed, 21 Oct 2009 21:54:55 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Benjamin LaHaise <bcrl@...et.ca>
CC:	Octavian Purdila <opurdila@...acom.com>, netdev@...r.kernel.org,
	Cosmin Ratiu <cratiu@...acom.com>
Subject: Re: [PATCH] net: allow netdev_wait_allrefs() to run faster

Benjamin LaHaise a écrit :
> On Wed, Oct 21, 2009 at 05:40:07PM +0200, Eric Dumazet wrote:
>> Ben patch only address interface deletion, and one part of the problem,
>> maybe the more visible one for the current kernel.
> 
> The first part I've been tackling has been the overhead in procfs, sysctl 
> and sysfs.  I've got patches for some of the issues, hacks for others, and 
> should have something to post in a few days.  Getting rid of those overheads 
> is enough to get to decent interface creation times for the first 20 or 30k 
> interfaces.
> 
> On the interface deletion side of things, within the network code, fib_hash 
> has a few linear scans that really start hurting.  trie is a bit better, 
> but I haven't started digging too deeply into its flush/remove overhead yet, 
> aside from noticing that trie has a linear scan if 
> CONFIG_IP_ROUTE_MULTIPATH is set since it sets the hash size to 1.  
> fn_trie_flush() is currently the worst offender during deletion.

Well, there are many things to change...

# ip -o link | wc -l
13097
# time ip -o link show mv22248
13045: mv22248@...3: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN \    link/ether 00:1e:0b:8e:c8:08 brd ff:ff:ff:ff:ff:ff

real    0m0.840s
user    0m0.473s
sys     0m0.368s

almost one second to get link status of one particular interface :(
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